This invention relates to white coatings, of the paint type, which are conductors of electricity.
In space engineering there is a need for coatings which are conductors of electricity and which have the following properties:
.alpha..sub.s (solar absorption).ltoreq.0.30
.epsilon.(hemispherical emission factor).gtoreq.0.80
Surface resistance R.sub.S (measured in a vacuum less than 10.sup.-5 torr).ltoreq.10.sup.9 ohms/square and which, in addition, meet the degasification-pollution requirements. That is, the requirements are that a sample of the coating submitted to a temperature of 125.degree. C. in a vacuum less than 10.sup.-5 torr for 24 hours should not undergo a weight loss greater than 1% and that the condensable products collected on a disc maintained at a temperature of 25.degree. C. should not be greater than 0.1%.
Such coatings are required for the thermal control of certain satellites, in particular geostationary satellites, and also for avoiding the accumulation of electric charges on these satellites due to irradiation by electrons or protons. White paints which are already known for applications in space do not have all these properties since they are electrically insulating (R.sub.S of the order of 10.sup.12 ohms/square).
The only known coatings which comply with all these properties, but which are not paints, can be classified within the following three types:
fabrics of quartz with or without a coating which is a conductor of electricity (doped indium oxide);
substrates of plastics material metallized on their inner surface and coated with a thin layer of doped indium oxide or tin oxide on their outer surface, these substrates being referred to as SSM (second surface mirror);
glass substrates (for example containing cerium) coated with a layer of doped indium oxide or tin oxide, these substrates being referred to as OSR (optical surface reflector).
The main disadvantage of these coatings is that they are very costly, as involving a very complicated technology.
It would therefore be advantageous to have electrically conductive white coatings of the paint type, which are easy to produce and inexpensive.